Problem: Simplify the following expression: $x = \dfrac{5r}{6} - \dfrac{r}{7}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $6$ and $7$ $\lcm(6, 7) = 42$ $ x = \dfrac{7}{7} \cdot \dfrac{5r}{6} - \dfrac{6}{6} \cdot \dfrac{r}{7} $ $x = \dfrac{35r}{42} - \dfrac{6r}{42}$ $x = \dfrac{35r -6r}{42}$ $x = \dfrac{29r}{42}$